Conventionally, a polyester cord made of polyethylene terephthalate (PET) or the like is used for a carcass cord, a twisted cord of fine yarn having a small total decitex at a high end count, or a twisted cord of thick yarn having a large total decitex at a low end count is individually used. Further, when a high treat tenacity is required, a plurality of the treats are used.
On the other hand, in recent years, because, in place of a tire for lightweight trucks, a tire for passenger cars comes to be used as a tire for SUVs, and because standardization of extra-load (XL) of a tire is being established accompanied with increase in the weight of a car, which is a trend of passenger cars and with increase in demand for the usage thereof at high speed traveling, there are some cases where the durability of the tire considerably deteriorates even when a two-carcass configuration employing a treat which has been used with no trouble is applied. On the other hand, however, when a configuration in which three or more treats are used is applied, a considerable increase in weight is accompanied with deterioration of rolling resistance.
As an improvement technique for a pneumatic radial tire employing a polyester cord as a carcass ply, for example, in Patent Documents 1 and 2, disclosed are techniques, in order to provide a pneumatic radial tire which has an excellent drivability, riding comfort and abrasion resistance, as well as an improved durability performance, a specific steel cord is used as a belt cord, and at the same time, a cord whose cord strength after adhesive treatment is 4.5 cN/dtex or higher, and whose bending rigidity per one cord is 15 to 50 cN is used as a polyester cord used for a carcass ply.